Add shader hot-reloading for real-time development

[code-alchemist01]

Is your feature request related to a problem?
Currently, when modifying shaders, you need to restart the entire application to see changes. This slows down development and experimentation.

Describe the solution you'd like
Add hot-reloading functionality that:

• Watches shader files in assets/shaders/ for changes
• Automatically recompiles and reloads shaders when files are modified
• Shows compilation errors in the console or UI
• Allows real-time shader tweaking without app restart

Describe alternatives you've considered

• Manual restart (current method) - too slow
• External shader editors - not integrated with the engine

Additional context
This would greatly improve the development workflow for visual effects, lighting, and material creation. Many modern engines like Unreal and Unity have this feature.

Files to modify: src/core/Shader.cpp, src/core/Shader.hpp